Oyster reefs are among the most valuable and vulnerable marine habitats worldwide in terms of ecosystem services. More interests in restoring coastal habitats of high importance have developed substantially in many regions. However, basic information on the structure and distribution characteristics of oyster populations in natural oyster reefs along the Chinese mainland coasts is still limited, even though it is crucial for establishing ecological reference baselines for evaluating oyster reef restoration. In recent years, a natural live oyster reef has been discovered in the intertidal zone near the mouth of the Xiaodaohe River, southwest of the Yellow River Estuary. As the oyster reef has been commercially harvested on a large scale, it is necessary and urgent to carry out effective conservation and restoration efforts. By surveying the exposed oyster reef in November 2021, this study investigated the species composition, age structure, and growth characteristics of the oyster populations on the reef. Based on morphological and molecular analyses, two oyster species were identified, including the Jinjiang oyster Crassostrea ariakensis and Pacifica oyster Crassostrea gigas. Only 6.1%-6.7% of the oysters sampled were dead oysters. The density and biomass of live oysters were (2811±778) ind./m² and (21.97±30.43) kg/m², respectively. Of the two species, C. ariakensis had higher density and biomass, accounting for 55.7% and 76.4% of the total live oyster density and biomass, respectively. In addition, the annual growth line on the shell cross-section indicated that the ages of oyster C. ariakensis ranged from 0+ to 4+ years, and those of C. gigas ranged from 0+ to 2+ years. Mean values of shell height, length, and inflation of C. ariakensis were relatively higher than those of C. gigas at the same age. Both oyster species were dominated (>80% in number) by young individuals of 0+ years old, with shell heights between 30-40 mm and shell masses less than 5 g. They also exhibited similar negative allometric growth patterns due to their individual linearly fitted model coefficients for shell mass and height <3. The ratios of individuals' shell height/ length and shell height/ inflation reflected differences in shell expansion between the two oyster species at different ages. According to the fitted von Bertalanffy (VB) population growth models of the two species, the estimated asymptotic shell height (SH_max) and inflection growth age (t_tp) for C. ariakensis were 286 cm and 5.47 years, respectively, with an asymptotic shell mass (W_max) of 812 g, the SH_max and t_tp for C. gigas were 173 cm and 2.56 years, respectively, with a W_max of 129 g. The test of covariance revealed that the distributions of fitted VB growth curves in the two species were significantly different (P<0.001). Therefore, it can be inferred that the oyster populations in the natural oyster reef were characterized by high density, young age, and low mortality, implying that the natural oyster reef was relatively rich in oyster resources. The present oyster populations could provide potential capacity for reef expansion and restoration near the mouth of the Xiaodaohe River, southwest of the Yellow River Estuary. Owing to its higher shell mass and growth, the oyster species C. ariakensis may hold greater importance than C. gigas in shaping and nurturing the natural oyster reef. An in-situ conservation, restoration, and long-term (the cycle >3 years) monitoring program is recommended for this oyster reef and oyster population.